Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $126.51   12.263%   $142.0239   $142.02   $142.00   $142.00  
  Purchase #2 $106.30   12.790%   $119.8958   $119.90   $119.90   $119.90  
  Purchase #3 $250.75   6.478%   $266.9936   $266.99   $267.00   $267.00  
  Purchase #4 $170.25   6.631%   $181.5393   $181.54   $181.55   $181.50  
  Purchase #5 $233.53   11.615%   $260.6545   $260.65   $260.65   $260.70  
  Purchase #6 $239.26   13.472%   $271.4931   $271.49   $271.50   $271.50  
  Purchase #7 $210.82   7.441%   $226.5071   $226.51   $226.50   $226.50  
  7 purchase totals = $1,337.42       $1,469.1073   $1,469.10   $1,469.10   $1,469.10